<style>
    .box1 {
        background-color: antiquewhite;
        width: 300px;
        height: 200px;
    }

    .box2 {
        background-color: aqua;
        width: calc(50% - 10px);
        height: calc(50% - 20px);
    }
    .box3{
        background-color: aquamarine;
        width: 50%;
        height: 50%;
        margin-top: 20px;
    }

    .sizeReference12 {
        font-size: 12px;
    }

    .sizeReference16 {
        font-size: 16px;
    }

    .sizeMax {
        font-size: max(2vw, 16px);
    }
</style>

<div class="box1">
    <div class="box2"></div>
    <div class="box3"></div>
</div>
<p>
    <span class="sizeReference12">演示文字14px</span>
    <span class="sizeReference16">演示文字16px</span>
</p>
<p>
    <span class="sizeMax">Max文字</span>
</p>